The present invention relates to a radio communication system for specifying a predetermined reference azimuth and then obtaining azimuth information on the basis of the specified reference azimuth, and more particularly to a ratio communication system suitably used for an ad hoc network.
In a radio communication system including a plurality of mobile units, azimuth information to specify a moving direction or a transmitting direction of radio waves is provided to the mobile units which freely move in a service area. The azimuth information can be used to select a path to a target place together with positional information. The azimuth information is used so that various systems may coexist. In other words, since the transmitting direction of radio waves is controlled on the basis of the azimuth information, interference with other systems can be reduced, so that a plurality of systems can coexist easily.
As a technique for providing the foregoing azimuth information, GPS (Global Positioning System) has been known. In the GSP, each mobile station receives a signal from a satellite using a GPS receiver to measure its own position or time. The mobile station can obtain azimuth information from the result of measurement.
The mobile station can obtain azimuth information using a gyro. On the other hand, a fixed station can obtain azimuth information so long as a direction is set when the fixed station is installed.
In a conventional method for obtaining azimuth information as mentioned above, the mobile station needs to have the GPS receiver or the gyro. Accordingly, there are disadvantages in that the size of a unit is large and a manufacturing cost also increases.
The present invention is made in consideration of the above actual situation. It is an object of the present invention to provide a mobile terminal unit serving as a mobile station unit which can obtain azimuth information with a simple constitution, a radio communication system having the mobile station unit, and an azimuth determining method.
According to the present invention, there is provided a radio communication system comprising a reference station which transmits an azimuth designation signal having directivity toward a previously set reference azimuth, and a plurality of terminal stations, wherein a target terminal station, included in the plurality of terminal stations, comprises receiving means which receives the azimuth designation signal transmitted from the reference station, arrival direction obtaining means which obtains an arrival direction of the received signal, azimuth designation signal generating means which generates an azimuth designation signal having directivity in the direction opposite to the arrival direction of the azimuth designation signal, and transmitting means which transmits the azimuth designation signal generated by the azimuth designation signal generating means.
According to this construction, since the reference station included in the radio communication system transmits the azimuth designation signal toward the reference azimuth, the arrival direction of the azimuth designation signal transmitted toward the reference azimuth is obtained to specify the reference azimuth, so that azimuth information can be obtained. Consequently, the radio communication system can be constructed without providing a GPS receiver or the like for the terminal station.
According to the present invention, in the radio communication system, the receiving means is constructed so as to receive the azimuth designation signals transmitted from the reference station and another terminal station.
According to this construction, the reference station and the terminal stations transmit the azimuth designation signals, thereby constructing an independently distributed system. As mentioned above, since the terminal station transmits the azimuth designation signal, the terminal station can specify the reference azimuth accurately.
According to the present invention, in the radio communication system, the target terminal station comprises reference azimuth specifying means which detects a direction of the directivity of the azimuth designation signal generated by the azimuth designation signal generating means as a reference azimuth.
According to this construction, the reference station and the terminal stations, included in the radio communication system, transmit the azimuth designation signals toward the reference azimuth. Accordingly, the arrival directions of the azimuth designation signals transmitted toward the reference azimuth are obtained to specify the reference azimuth, so that azimuth information can be obtained. Consequently, the azimuth information can be obtained without providing a GPS receiver or the like. The construction of a unit serving as the terminal station can be miniaturized and a manufacturing cost of the unit can be reduced.
According to the present invention, in the radio communication system, the reference azimuth is set in the longitudinal direction of a service area of the radio communication system.
According to the present invention, in the radio communication system, the reference station is installed along a road and the reference azimuth is set in a direction along the road.
According to the constructions, the reference azimuth is appropriately set in accordance with the form of the service area. Accordingly, the number of azimuth designation signals to be received by the terminal station included in the system can be larger than that of a case where the reference azimuth is set in another direction. Therefore, the reference azimuth can be detected accurately.
According to the present invention, the radio communication system further comprises means which detects a reference plane to be referred when a communicating direction is determined.
According to this construction, a transmitting direction of the azimuth designation signal can be determined in consideration of a transmitting direction on the reference plane. Consequently, correct azimuth information can be obtained.
According to the present invention, in the radio communication system, each of the reference station and the plurality of terminal stations adds priority information to the azimuth designation signal and then transmits the resultant signal, and the azimuth designation signal generating means weights the plurality of received azimuth designation signals in accordance with the priority information to generate the azimuth designation signal.
According to this construction, the arrival directions are weighted in accordance with the priorities of the azimuth designation signals to determine the arrival direction of the azimuth designation signal, so that the arrival direction can be determined accurately. Consequently, since the reference azimuth can be detected accurately, the accuracy of the obtained azimuth designation also increases.
According to the present invention, the radio communication system further comprises priority adding means which adds priority to the azimuth designation signal, the priority decreasing each time transmission is performed.
According to the construction, since the priority is decreased each time the azimuth designation signal is transmitted, a deviation in the transmitting direction from the reference azimuth can be reduced, the deviation being caused by repeating the transmission of the azimuth designation signal.
According to the present invention, in the radio communication system, the target terminal station comprises averaging means which averages the arrival directions obtained by the arrival direction obtaining means, and the azimuth designation signal generating means generates an azimuth designation signal having directivity in the direction opposite to the averaged arrival direction.
According to the construction, since the transmitting direction is determined on the basis of the average of the arrival directions, the arrival direction can be obtained accurately. Therefore, the terminal station can accurately detect azimuth information and can also correctly transmit radio waves carrying the azimuth designation signal toward the reference azimuth. Consequently, the accuracy at which the azimuth is detected increases in the whole system.
According to the present invention, in the radio communication system, the terminal station comprises means which extracts an electric power from the azimuth designation signal.
According to the construction, the electric power can be transmitted to the terminal station using the azimuth designation signal.
According to the present invention, in the radio communication system, the terminal station comprises means which extracts an electric power from the azimuth designation signal. According to the present invention, in the radio communication system, the terminal station comprises means which superimposes an electric power on the azimuth designation signal.
According to the constructions, the electric power can be transmitted to the terminal station using the azimuth designation signal. Consequently, continuous available time derived by charging once extends, so that the system becomes more convenient to the user.
According to the present invention, the radio communication system comprises a charging management unit comprising a management table which holds communicating situations of the plurality of terminal stations, and a charge determining section which determines a charge for each terminal station with reference to the management table in accordance with the communicating situation of the corresponding terminal station.
According to the construction, since the charge can be determined in accordance with the communication situation of each terminal station, the system can be operated efficiently. For example, the terminal station which transmits the azimuth designation signal is released from a charge. Releasing from the charge as mentioned above results in an incentive to transmit the azimuth designation signal for the terminal station. Consequently, since many transmission sources of the azimuth designation signals can be held in the system, azimuth information can be obtained using the azimuth designation signal in a wide range of the service area of the system.
According to the present invention, there is provided an azimuth determining method for determining an azimuth in a terminal station, comprising the steps of: in a reference station, transmitting an azimuth designation signal so as to form directivity toward a previously set reference azimuth; and in the terminal station, receiving the azimuth designation signal in the terminal station, obtaining an arrival direction of the azimuth designation signal, generating an azimuth designation signal having directivity in the direction opposite to the obtained arrival direction, transmitting the generated azimuth designation signal, specifying a reference azimuth on the basis of the arrival directions of the azimuth designation signals transmitted from the reference station and the terminal station, and determining an azimuth on the basis of the specified reference azimuth.
According to the method, since the reference station and the terminal station, included in the radio communication system, transmit the azimuth designation signals toward the reference azimuth, the arrival directions of the azimuth designation signals transmitted toward the reference azimuth are obtained to specify the reference azimuth, so that azimuth information can be obtained. Consequently, since the azimuth information can be obtained without providing a GPS receiver or the like, the construction of a unit serving as the terminal station can be miniaturized and a manufacturing cost of the unit can be reduced.
According to the present invention, there is provided a mobile terminal unit comprising: receiving means which receives an azimuth designation signal, which is transmitted from a reference station so as to form directivity in a previously set reference azimuth; arrival direction obtaining means which obtains an arrival direction of the received signal; azimuth designation signal generating means which generates an azimuth designation signal having directivity in the direction opposite to the arrival direction of the azimuth designation signal; reference azimuth specifying means which detects the direction of the directivity of the azimuth designation signal generated by the azimuth designation signal generating means as a reference azimuth; and transmitting means which transmits the azimuth designation signal generated by the azimuth designation signal generating means.
The receiving means receives an azimuth designation signal transmitted from another mobile communication terminal unit, and the arrival direction obtaining means obtains an arrival direction of the azimuth designation signal transmitted from the other mobile terminal unit.
According to the construction, the arrival direction of the azimuth designation signal transmitted toward the reference azimuth is obtained to specify the reference azimuth, so that azimuth information can be obtained. Consequently, since the azimuth information can be obtained without providing a GPS receiver or the like, the construction of the unit can be miniaturized and a manufacturing cost of the unit can be reduced.